High intensity discharge luminaires, hereinafter referred to as HID luminaires, as well as fluorescent, and incandescent luminaires are commonly installed at high locations at commercial or industrial facilities such as on the ceiling of a warehouse or plant, or on light poles in a parking lot or stadium. In addition, HID luminaires can include, but are not limited to, metal halide (MH) lamps, and high pressure sodium (HPS) lamps. Some MH luminaires and all HPS luminaires use pulses from a high voltage source such as an ignitor circuit to ignite the lamp.
In many applications, the HID, fluorescent, and incandescent luminaires can be elevated on the order of thirty feet or more above the ground or floor of a commercial or industrial facility. The elevation of the luminaires makes servicing inconvenient and time consuming since service personnel must ascend to considerable heights in order to gain access to the luminaires, assess the problem and then repair or replace the defective components. Since the lamps in a luminaire are frequently the defective component, it would be useful to provide spare lamps in a luminaire that are automatically switched on as needed, thereby reducing the need to replace these components. Therefore, a need exists for increasing the serviceable life of a fluorescent, high intensity discharge, or incandescent luminaire by connecting multiple lamps to a single ballast, yet allowing one lamp to operate at any given time. Accordingly, a luminaire that requires lamp maintenance every 8000 hours is transformed into a luminaire that is serviced every Nxc3x978000 hours, where N is the number of lamps coupled to the single ballast, and limited by the physical capacity of the luminaire.
U.S. Pat. No. 3,790,846 by Morris discloses an automatic load monitoring and transfer circuit and is representative of the conventional methods for increasing luminaire service life. The apparatus disclosed in U.S. Pat. No. 3,790,846 automatically switches to the secondary load, upon failure of the primary load, thereby extending luminaire service time by twice that of a typical incandescent luminaire. The apparatus disclosed in U.S. Pat. No. 3,790,846, however, employs an incandescent luminaire and does not have the necessary internal circuitry to facilitate operation of a fluorescent or, a HID luminaire. In addition, the apparatus disclosed in U.S. Pat. No. 3,790,846 ensures that the primary load is activated before the secondary load via phase shifting a load current, thus facilitating proper sequencing of the loads. Accordingly, the invention disclosed in the Morris patent is not equipped to operate with more than two incandescent lamps. Therefore, a need exists for an apparatus for operating respective ones of a plurality of incandescent, fluorescent or, high intensity discharge luminaires.
The present invention overcomes the deficiencies of existing devices that enable operation of a selected lamp, and realizes a number of advantages over these devices. An apparatus for operating one of a plurality of lamps is provided in accordance with the present invention that extends the service life of the luminaire, by operating one lamp, therein, at a given time.
In accordance with an aspect of the present invention, the lamp selection apparatus is employed within a luminaire comprising a single ballast for a plurality of lamps therein. This allows the luminaire service life to be extended, at least by the number of lamps within the luminaire.
In accordance with another aspect of the present invention, the lamp selection apparatus is configured such that it does not allow multiple lamp rectification. In other words, specific components are provided in the present invention that inhibit the upstream lamps from turning on and off in an alternating half-wave sequence.
In accordance with an aspect of the present invention the lamp selection circuitry is configured to be operable for multiple lamp types. For example, the present invention employs fluorescent luminaires.
In accordance with an aspect of the present invention, the apparatus for operating one of a plurality of lamps via a single ballast comprises a rectifying circuit and a gating circuit. The plurality of lamps are connected in parallel and comprise the operating lamp and any upstream lamps connected between the operating lamp and the ballast and any downstream lamps connected on the other side of the operating lamp. The rectifying circuit rectifies the lamp current from the operating lamp that provides illumination. The gating circuit then stops conduction of any downstream lamps, ensuring operation of a single lamp.
Another embodiment of the apparatus incorporates the rectifying circuit and the gating circuit, as well as a capacitive circuit. In this embodiment, the plurality of lamps comprise the operating lamp and all upstream lamps, that is, those lamps between the ballast and the operating lamp, and the downstream lamps. The capacitive circuit is placed in series with the output of each of the lamps to store energy associated with the rectified current and reduce the associated voltage from the ballast to the upstream lamps. This embodiment is provided to inhibit multiple upstream lamps from rectifying, thus turning on and off in an alternating half-cycle sequence.
The present invention also provides a method for operating one of a plurality of lamps via a single ballast. The method comprises, first, rectifying a signal through one or more rectifying circuits from an operating lamp, thereby conditioning the signal for use as a gating signal. Gating of the associated thyristors is then performed to prevent operation of the lamps connected downstream from the operating lamp.
In accordance with another embodiment, the method comprises the steps of rectifying and gating the signal, as well as, storing energy in the capacitive circuit from the one of the lamps connected upstream from the operating lamp. In addition, a reverse voltage is provided by the capacitive circuit, with respect to the ballast, thus reducing the voltage across each of the upstream lamps. The lamps subsequently extinguish as a result of the reduced voltage until only one of the lamps remains in an operational state.